The present invention relates to a wavelength division multiplexing optical transmission system and, more particularly, to an art for selecting a signal light of any desired channel therein.
In an optical communication field, a wavelength division multiplexing (WDM) optical transmission system has been studied for systematizing a large capacity communication system allowing for a large transmission capacity. This transmission system through wavelength division multiplexing is provided with a plurality of signal light sources, each of the signal light sources has a different wavelength in order to increase the signal transmission capacity. The signal speed of each channel is independently set, which has been highly expected to be put into an industrial use in near future.
FIG. 3 is a block diagram of a construction of a conventional wavelength division multiplexing optical transmission system as described above.
In FIG. 3, signal light sources 2-1 to 2-n are provided with the respective channels for generating signal lights having different wavelength .lambda.1 to .lambda.n corresponding to the respective channels.
A reference numeral 8 is a modulator for data modulating the signal light sources 2-1 to 2-n.
A reference numeral 3 is a multiplexer comprising a coupler or the like for wavelength multiplexing each signal light having different wavelength .lambda.1 to .lambda.n, which is transmitted to an optical transmission path 4 consisting of an optical fiber.
A reference numeral 5 is a wavelength division unit for dividing the wavelength of the wavelength multiplexing light via the optical transmission path 4.
Reference numerals 6-1 to 6-n are filters for receiving each wavelength multiplexing light which has been wavelength divided in the wavelength division unit 5. In accordance with the wavelength ranging from .lambda.1 to .lambda.n of the respective filters 6-1 to 6-n, the signal light of a predetermined wavelength is selectively permeated.
Reference numerals 7-1 to 7-n are optical detectors for receiving outputs of the corresponding filters 6-1 to 6-n, respectively. The optical detectors 7-1 to 7-n detect the signal light of the predetermined channel (wavelength).
In the above-constructed wavelength division multiplexing optical transmission system, each of filters 6-1 to 6-n at a reception section is preliminarily set and fixed to have a wavelength selection characteristic so as to select a signal light of a predetermined channel. In the conventional transmission system as described above, light sources 2-1 to 2-n at a transmission section and optical detectors 7-1 to 7-n at a reception section are fixedly correlated and defined by the wavelength selection characteristics of filters 6-1 to 6-n. Once each correlation between the light source and the optical detector is defined, any further selection of the desired correlation is not allowed.